The present invention relates generally to syringes for administering liquid and semi-liquid (e.g. pastes) compositions and preparations such as medicines, pharmaceuticals and the like. The invention is more particularly directed to syringes adapted to discharge material in a plurality of separate successive, preselected dosages which may vary in quantity from each other, or which may be of the same quantity. The invention is particularly useful in connection with the administration of veterinary paste, such as that commonly administered to horses, but is not limited to this specific application.
U.S. Pat. No. 3,563,240, entitled "Dual Unit Syringe" and issued to Jules Silver on Feb. 16, 1971, is illustrative of the general state of the art. This patent discloses a syringe including a container pre-loaded with material to be administered, and a plunger received within the container for discharging separate, predetermined quantities of material from a discharge opening in the container. A scale inscribed on the plunger enables the user to select a predetermined dosage of material to be discharged from the container. The plunger includes a threaded outer surface, and a nut or other stop element is rotatable along the plunger relative to the scale on the plunger. The scale designates predetermined dosages to be administered, and the nut is moved into alignment with a desired dosage designation. The plunger is then advanced into the container until further forward movement of the plunger is prevented by the stop element abutting against the rear end of the container. Engagement of the stop against the container to restrain further forward movement of the plunger indicates that the desired preselected dosage of material has been discharged from the syringe. The scale provided on the plunger designates specific predetermined dosages, but does not indicate the specific quantity of material to be discharged from the syringe. Accordingly, any variation in the quantity of material to be discharged which differs from the preset doses designated on the scale must be based upon imprecise estimates.
PCT Patent Specification No. PCT/US80/01468 (corresponding to U.S. Pat. No. 4,275,329, issued Jun. 30, 1981) discloses a syringe (marketed under the name DIAL-A-DOSE) including a scale on a plunger designating specific quantities of material to be discharged. A stop element is formed from a ring which is slideable along the plunger to select the next desired dose to be administered by the syringe. The ring is rotatable into a locked position on the plunger after the desired dose has been set. However, after an initial dose is discharged, subsequent doses only can be set on the scale after calculations have been made based upon the quantity of material previously discharged from the syringe. For example, if the first dosage to be administered is "50" in quantity, the portion of the scale designating "50" will be aligned with the rear end of the container after the plunger has been advanced relative to the container to discharge the initial dose. The scale setting of a subsequent dosage to be administered must be based on calculations using "50" as the standard of reference. If, for example, the next dosage to be administered is "75" in quantity, the user must make a calculation to determine the total quantity that will have been discharged after the next dosage has been administered, and then retract the stop means to "125" on the scale of the plunger to assure that a quantity of "75" will next be discharged from the syringe. Continuous re-calculating, re-adjusting and re-setting the position of the stop means on the scale for each subsequent dose to be administered from the syringe is cumbersome, adversely affects the time required for administration, and is likely to result in errors in the dosages administered, particularly where numerous dosages of different quantities are to be sequentially administered.
A syringe sold under the name SLIDE-A-DOSE and marketed by Silver Research (and more fully described in U.S. Pat. No. 5,009,645, issued Apr. 23, 1991) similarly includes a scale on a plunger which requires continuous calculations based on the quantity of previously administered doses as a prerequisite to setting the next successive dose to be administered. Accordingly, the drawbacks discussed with reference to the aforementioned PCT publication, are equally applicable to this syringe. The SLIDE-A-DOSE syringe employs a stop element which is slideable along the scale of the plunger and held in a selected position thereon substantially by a knife edge carried by the stop and depressed to become embedded in a rail defined on the plunger. The knife edge is disengaged by rotatably moving the stop relative to the plunger.
It is the primary object of the present invention to provide a syringe having a scale which is automatically re-set to a zero reference position after any preselected dosage of material has been discharged from the syringe. The automatic-zero reset enables the user to set the scale for only the quantity of material to be discharged from the syringe for the next dosage to be administered, thereby eliminating the need to make calculations and adjustments to the setting on the scale to compensate for the quantity of material discharged from the syringe in prior doses. In this manner, separate, multiple dosages of material, each of which may (or may not) vary in quantity from each other, can be efficiently administered from the same syringe, thereby improving the overall efficiency of the administration procedure and eliminating the risk of administering an incorrect dosage as a result of erroneous calculations or scale settings by the user.
It is a further object of the present invention to provide a syringe for administering separate, multiple dosages of material including improved means for setting the preselected quantity of material to be administered, improved means for assembling a scale within the plunger, improved means for storing a retainer cap or closure element for the discharge outlet of the syringe when the cap is removed from the discharge outlet, and improved means for assuring that substantially the entire contents of the syringe is ultimately discharged therefrom to minimize any residue therein.
Other objects and advantages of the present invention will become apparent from the following description.